In a cellular radio network system, the size of cells may vary according to the predicted traffic amount of an area, for instance. In a sparsely populated area, the cells often are large macro cells, whereas in population centres, the reuse of frequencies must be more efficient, which aim is reached by reducing the size of cells, i.e. by using micro or pico cells. A micro cell covers a multi-storey office building, for instance, or a section of a street, whereas a pico cell covers an area of a few offices inside a building, for instance. The diameter of a pico cell is typically from a few meters to a few dozen meters, while the transmission power level of the base station is a few dozen or hundred milliwatts, the size of a micro cell is in the range of 10 to 400 meters, and macro cells may be several kilometres in size, while the transmission power level is dozens of watts.
In practise, the structure of cellular radio networks in population centres are often such that a network formed by macro cells, such as a GSM network (890 to 915 MHz in uplink direction and 935 to 960 MHz in downlink direction), uses a different frequency band than a micro cell network, such as a DCS network (1710 to 1785 MHz in uplink direction and 1805 to 1880 MHz in downlink direction), whereby the traffic of one network does not cause interference to that of the other.
Frequency planning becomes, however, more complicated if networks using the same frequency range have overlapping coverage areas having different cell sizes. Such a situation arises, for instance, when office base station networks comprising micro or pico cells and operating on GSM frequencies operate on the coverage area of a GSM network comprising macro cells and operating in a densely populated area. One solution to using frequencies in such a situation is to allocate a certain frequency range to the macro cell network and another to the micro cell network from the frequency band allocated to the GSM network. Alternatively, the micro cell network can be implemented in such a manner that the channels it requires are dynamically borrowed from temporarily unused channels of the macro cell network. With respect to the capacity of the macro cell network, neither solution leads to a satisfactory result.
The frequency planning of a micro cell network can also be implemented using fixed channel allocation (FCA) and the same frequency space with the macro cell network, whereby the operation of the micro cell network must be ensured by careful frequency planning so as to prevent the macro cell network which has a higher transmission power level from causing interference to the traffic of the micro cell network. Especially in situations where changes are made to the frequency usage of the macro cell network, the operation of the micro cell network must be ensured by a fast re-planning and re-selection of frequencies and a network operation testing combined to them. Today, the testing of the frequency set to be used is, in practice, done manually by measurement personnel. The drawback is that the testing is slow and laborious, for instance in measurements done at night or repeated regularly.